Modern Engineering Thermodynamics

526 CHAPTER 13: Vapor and Gas Power Cycles
Table 13.3 Summary of Power Cycle Thermodynamic Processes
Cycle Name
Cycle Process
Carnot (1820) Two constant entropy and two constant temperature processes (2s and 2T )
Rankine (1859)
Two constant entropy and two constant pressure processes (2s and 2p), mostly under the vapor dome
Stirling (1816) Two constant temperature and two constant volume processes (2T and 2V )
Ericsson (1833) Two constant temperature and two constant pressure processes (2T and 2p)
Lenoir (1860) One constant entropy, one constant volume, and one constant pressure process (1s, 1V, and 1p)
Brayton (1873) Two constant entropy and two constant pressure processes (2s and 2p)
Otto (1876) Two constant entropy and two constant volume processes (2s and 2V)
Atkinson (1885) and
Miller (1947)
Two constant entropy, one constant volume, and one constant pressure processes (2s, 1V, and 1p)
Diesel (1893) Two constant entropy, one constant volume, and one constant pressure processes (2s, 1V, and 1p)
The field of power plant thermodynamics is so broad that it is difficult to present it adequately in just one chapter.
In this chapter, we attempt to find a new course for its presentation by carefully charting the chronology of
its development. Our goal is to provide you, the reader, with a historical perspective on this important technology
and historical benchmarks with which to judge the significance of its impact on society and to broaden
your understanding of your chosen profession. Contrary to the opinion held by most historians, the history
of the human race is primarily a history of its technological development, with the social faux pas of the ruling
aristocracy being much less significant than the concurrent advances in mathematics, metallurgy, mechanics, and
so forth.
Some of the more important equations introduced in this chapter follow. Do not attempt to use them blindly
without understanding their limitations. Please refer to the text material where they were introduced to gain an
understanding of their use and limitations.
1. The thermal efficiency of a steam engine whose output is rated in duty is
Duty
η T ðin%Þ =
8:50 × 10 8 × 100
2. The thermal efficiency of an engine operating on a Carnot vapor power cycle is
ðη T Þ Carnot
= 1 − T L /T H
where T L and T H are the high and low temperature limits of the cycle.
3. The thermal efficiency of a Rankine cycle power plant without regeneration or reheat is
ð
ðη T Þ Rankine = h 1 − h 2s Þðη s Þ pm
− v 3 ðp 4 − p 3 Þ/ ðη s Þ p
h 1 − h 3 − v 3 ðp 4 − p 3 Þ/ ðη s Þ p
Note that the maximum (or isentropic) thermal efficiency of this cycle occurs when (η s ) pm = (η s ) p = 1.0.
4. The thermal efficiency of a Rankine cycle with one stage of regeneration is
ðη T Þ Rankine cycle
= 1 − h
2 − h 3
ð1 − yÞ
h 7 − h 6
with 1 regenerator
ðeither open or closedÞ
5. The thermal efficiency of a Rankine cycle with one stage of reheat is
ðη T Þ Rankine
cycle with
one reheat unit
W
= _ pm − j _W p j ð
= h 1 − h 2 Þ+ ðh 3 − h 4 Þ− ðh 6 − h 5 Þ
_Q B + _Q R
ðh 1 − h 6 Þ+ ðh 3 − h 2 Þ
where h 2 = h 1 – (h 1 – h 2s )(η s ) pm1 and h 6 = h 5 + v 5 (p 6 – p 5 )/(η s ) p , and of course p 6 = p 6s .
6. The thermal efficiency of an engine operating on a Carnot gas power cycle is
ðη T Þ Carnot
= 1 − T L /T H = 1 − PR ð1−kÞ/k = 1 − CR 1−k
cold ASC
where PR is the isentropic pressure ratio and CR is the isentropic compression ratio.